Thread-chain cutting device for sewing machines



United States Patent [72] Inventor Hermann F. Daniel Stuttgart-Plieningen, Germany [21] App1.No. 760,183 [22] Filed Sept. 17, 1968 Nov. 24, 1970 Union Special Maschinenfabrik G.m.b.l'l. Stuttgart, Wuerttemberg, Germany [45] Patented [73] Assignee [32] Priority Sept. 23, 1967 I 3 1 Germany [31 1 No. 1,685,080

[54] THREAD-CHAIN CUTTING DEVICE FOR SEWING MACHINES 8 Claims, 5 Drawing Figs.

Primary Examiner-James R. Boler An0rney-H.C. Dieserud ABSTRACT: Thread-chain cutting mechanism for sewing machines involving a pair of knives disposed in a horizontal plane parallel to .the plane of the throat plate of the machine, at least one of said knives being swingable about an axis perpendicular to the plane of the throat plate. Operation of said swingable knife is produced by connections from a conventionally driven member of the machine, such as a feed bar. Pneumatic means are provided for urging a thread-chain, that is formed beyond the rearward edge of a work piece being stitched, into the zone of operation of the cutting mechanism.

Said means for urging the thread-chain into the zone of operation of the cutting knives involves the delivery of air under pressure toward the region in which the cutting knives operate. When the stitch forming mechanism involves two needles, one cooperating with means for producing an overedge line of stitches and the other a parallel line of through and through stitches, means are provided for directing two jets of air, one toward each of the free thread-chains, for urging the latter toward each other and into the cutting zone. The connections from said feed bar, or the like, to at least one of said knives which is swingable comprises bendable or otherwise distortable means adapted to convert the longitudinal movement imparted to one end thereof into an arcuate movement of the engaged portion of a member carrying said swingable knife.

Patented Nov. 24, 1970 Sheet 1 of 2 Sheet 2 of 2 IIJII This invention relates to a thread-chain cutting device for sewing machines, said device having a pair of knives located in a plane parallel to the plane ofthe throat plate ofthe machine, at least one of said knives being swingable about an axis perpendicular to the plane of the throat plate.

An important feature of the invention is the provision of connections from a member driven by the main drive shaft of the machine, during each cycle of operation of the machine, to a member carrying a swingable knife of the thread-chain cutting device. Heretofore it has been found necessary to operate thread-chain cutting means, disposed in the manner specified, by a separate power means. This has been due to the fact that no one has found it possible, heretofore, to provide connections from the main drive shaft of the machine to im'- part the necessary movement to at least one of the two horizontally disposed cutting knives.

Another feature-of the improved construction is the provision of air under pressure for moving the thread-chain, trailing from the end of the work piece being stitched, into the region in which the cutting means is effective. This aspect of the invention is made possible by continuously directing air under pressure toward the path of the trailing thread-chain in a manner to cause movement of the latter forwardly and downwardly between the cutting edges of the two knives which are located parallel to the plane of the throat plate and slightly lower than the latter. A portion of the thread-chain is thus brought into the path ofthe swingable knife so as to cause the latter, in cooperation with the other knife, to sever the thread-chain.

it has been an important object of the present invention to provide a drive connection for at least one of the two knives mentioned, for swinging the same by suitable connections from some driven part of the sewing machine, which is operated on each cycle of operation of the machine. In accordance with a preferred embodiment of the invention, the swingable knife is carried bya lever which is connected by a link with the feed barof the sewing machine. The link referred to has a bearing lug or element at each end, these being interconnected by a member, such as a leaf spring or the like, which enables relative movement of the bearing lugs into different planes. The lever which carries the swingable knife is preferably mounted on a supporting structure which carries the other parts of the cutting mechanism. in this way there is formed a compact unit which can be mounted on and adjusted independently of other parts of the sewing machine.

Other objects, features and advantages of the invention will appear from the detailed description of a preferred embodimerit of the same, which will now be given in relation to the accompanying drawings, in which:

FIG. 1 is a side view of the cutting mechanism and related parts shown as applied to an overedge sewing machine, a portion ofthe frame of which is shown in section;

FIG. 2 is a plan view ofthe mechanism shown in FIG. 1, and

illustrates the relationship of the cutting device to the throat plate ofthe machine;

FIG. 3 is a view, partly in plan and partly in horizontal section, showing a part of the supporting structure and the connections from the feed bar of the machine to the swingable knife blade;

FlG. 4 is a view similar to FlG. 2, but omits the showing of the means for supplying air to the thread-chain for shifting the latter into the cutting zone of the device, and

FIG. 5 shows a flexible link which serves to connect the lever which carries the movable knife blade with a driven part of the sewing machine, such as a feed bar.

The details of the sewing machine are not shown in the drawings, but it may suitably be of the character illustrated and described in detail in the patent to Wallenberg etal. US. Pat. No. 2,704,042, granted on March l5, i955. This is an overedge sewing machine of well-known character arranged to provide a multiple thread overedge seam along one edge of work being advanced through the machine. The invention may also be used in connection with a sewing machine adapted to form an overedge line of stitching, and in parallel therewith an adjacent line of two-thread chain-stitching. Such a machine may, for example, be of the character shown in the patent to Schweda et al. US. Pat. No. 2,973,730, granted March 7, 196i. 7

Turning now to the drawings, a tube 1 is provided for leading away, and delivering to a suitable disposal point, the cut thread-chain as it is severed by the cutting blades of the present invention. The end of this tubewhich is adjacent the throat plate 2 has a slightly inclined surface 3, in the path of the work being stitched and the free thread-chains trailing the -work. The tube 1 is fastened on a support 4 which is in turn fastened by screws 5 to the housing 6 of the sewing machine. Support 4 carries a blow tube 7 which extends from a source of air-under pressure and discharges this air in small streams through two nozzles 8 and 9 (FIGS. 1 and 2). A plate 13 (FIGS. 2 and 4) is mounted in a recess provided in the top of tube 1 and it is also fastened to the support 4 by means of screws 12. This plate has an edge forming a stationary knife. Also provided on the support 4 is a guide member 14. The vertically disposed surface of this member, which is adjacent the throat plate 2, serves to keep the edge of the material leaving the throat plate in a proper line.

Cooperating with the knife edge of plate 13 is a knife 16 which is fastened by a screw 18 in an adjustable manner to the upper surface of an arm 17;: of a bell crank lever 17. To enable adjustment of the knife 16, it is preferably provided with an elongated opening which receives the shank of screw 18. The bell crank lever 17 is mounted for rocking movement about the axis ofa hollow pin 19 which is rotatably mounted in projections 4a and 4b of the support 4. A set screw, or the like, may serve to retain the pin 19in fixed relation to the lever 17. A pin 20 (P10. 3) mounted in a recess in the arm 17b of the bell crank lever 17 serves to carry a bearing lug 22 provided at one end of a leaf spring 21. The opposite end of the latter is connected with a bearing lug 23 which surrounds a member 24 that is inthe form ofa round nut secured by ascrew 25 to feed bar26 ofthe sewing machine. This feed bar, it will be understood, carries the feed dog for advancing the work through the stitch forming region. The feed bar is given the usual four motion movements by the conventional connections from the main drive shaft of the machine, so as to impart the desired lifting and lowering and the feeding and return movements to a feed dog. The bearing lugs 22 and 23 together with the leaf spring 21 form a link which partakes of the movement of the feed bar 26 and transmits the longitudinal movement of the latter to the arm 17b of the bell crank lever 17. The resulting arcuate movement of the outer end of the lever arm 17b and the lifting and lowering of the feed dog are compensated for by the leaf spring 21, which bends for this purpose while the bearing lugs 22 and 23 are shifted into different angular relations to each other.

In the illustrated embodiment of the invention, the cutting device is employed in a sewing machine which in addition to forming an overedge seam also produces a double chain stitch seam in the manner hereinabove explained, and as shown in the patent to Schweda et al. referred to. For this reason the inclined surface 3, at the forward end of the tube 1, is provided with two inlet openings 28 which communicate with the interior of tube 1 and also with slots 29, the ends of which merge into each other and terminate in the wedge-shaped cutting zone formed by the knives 13 and 16. By bringing together the slots 29, in the manner shown and explained, the outermost edge of the material being stitched is supported in a particularly advantageous manner, and said edge is prevented from being blown into the tube or the slots therein.

it will be understood that in the operation of the sewing machine, successive work pieces will be fed along the throat plate and thread-chains will be produced between the trailing end of one work piece and the forward end of the next work piece.

While it has been found to be a highly desirable feature of the invention to blow the thread-chain or chains into the tube 1 by air under pressure. it is possible to cause the threadchains to follow the indicated paths by applying a suction action to the tube. Thus the outer end of the tube 1 may be connected with a suitable vacuum source to cause the threadchain or chains to be drawn into the end of said tube which is adjacent the throat plate, through the openings 28 and slots 29.

While a preferred embodiment of the invention has been described in some detail in the foregoing, it will be understood that various changes may be made in certain parts and features within the scope ofthe appended claims.

I claim:

l. A thread-chain cutting device in combination with a sewing machine having a frame, a throat plate and a driven part which comprises: a pair of knives lying parallel to the plane of the throat plate, at least one of said knives being swingable about an axis perpendicular to the plane of the throat plate, a lever, means securing said swingable knife to said lever, and a member connected at one end to said lever and at its other end to said driven part of the sewing machine for rocking said lever.

2. A thread-chain cutting device as set forth in claim 1 in which said driven part is a feed dog carrying member, and said member connected at one end to said lever is connected at its other end to said feed dog carrying member.

3. A thread-chain cutting device as set forth in claim 1 in which said memberis in the form ofa link having a bearing lug at each end of the main body thereof, said main body of said link and said bearing lugs being so formed and connected as to enable said bearing lugs to change their angular relation to each other while imparting a rocking movement to said lever.

4. A thread-chain cutting device as set forth in claim 3 in which the bearing lugs of said member are provided with flat outer surfaces and said lugs are so connected with said main body that said flat surfaces of said lugs may be readily shifted LII into different planes in relation to each other.

5. A thread-chain cutting device as set forth in claim 3 in which the main body of said member is a leaf spring to which said bearing lugs are rigidly connected.

6. A thread-chain cutting device on a sewing machine having a throat plate, said machine being adapted to form two lines of stitching, including an overedge line of stitching and a two-thread chain stitch line of stitching, which device comprises: a pair of knives having their cutting edges disposed in adjacent planes parallel to that of the upper surface of said throat plate ofthe sewing machine, means for swinging at least one of said knives in the plane of its cutting edge, means for directing jets of air toward and along the path of movement of free chains of thread formed at the trailing end of each work piece being stitched by said sewing machine, said jets of air being adapted to direct said free chains of thread trailing a work piece toward each other and towardthe plane of said cutting edges, means driven upon each cycle of operation of the sewing machine, and means connecting said driven means to said means for swinging at least one of said knives to carry its cutting edge into cooperative relation with said threadchains and with the other of said knives to sever said threadchains.

7. A thread-chain cutting device as set forth in claim i having a supporting member, means securing said supporting member to said frame of said sewing machine, said member carrying said knives and a tube adapted to receive the segments of thread-chain severed by said knives.

8. A thread-chain cutting device as set forth in claim I having an elongated tube extending rearwardly from said throat plate, one of said knives forming a part of the wall of said tube and the swingable knife extending into said tube, and means for blowing air toward the passage in said tube for delivering free chains of thread thereto in the path of movement of said swingable knife. 

